The defendant in a lawsuit must be served (delivered) a summons or citation (an order from the court to appear and answer the lawsuit) and a copy of the lawsuit (1) to provide due process (fairness) by giving the defendant notice of the lawsuit and the opportunity to appear in court and defend the lawsuit; and (2) to give the court personal jurisdiction (authority) over the defendant.
In Oregon, as in all states, the legal process requires that a defendant in a lawsuit must be properly served with a summons or citation and a copy of the complaint initiating the lawsuit. This is to ensure due process, which is the constitutional right to be informed of legal action against oneself and to have a fair opportunity to respond and present a defense. Service of process must be carried out in a manner prescribed by law, which typically includes personal delivery to the defendant, delivery to someone of suitable age and discretion at the defendant's residence, or sometimes by mail, depending on the rules of the court. Proper service of process is also necessary for the court to establish personal jurisdiction over the defendant, which is the court's authority to make legal decisions affecting the defendant. If a defendant is not properly served, they may not be bound by the court's decisions, and the lawsuit may be dismissed or delayed until service is correctly performed.